Interactions of nitric oxides, organic compounds, and particulate matter and their effects on air quality
Bean, Jeffrey Kevin
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New concerns over health effects and tightening EPA regulations are pushing policy-makers towards lower and lower levels of pollutants. In many places in the United States the EPA standards for ozone and particulate matter (PM) are difficult to meet. This concern is elevated as both standards have been tightened in recent years. Improvements to air quality are costly, and policy-makers rely on regional photo-chemical models to find the most effective methods of pollutant reduction. The accuracy of forecasted predictions of ozone and PM depends heavily on the interactions of NOx and organic compounds. An understanding of the interactions of NOx, organic compounds, and PM is necessary in three important and ongoing research areas: 1 – organic nitrate partitioning and hydrolysis, 2 – interactions between biogenic organic compounds with anthropogenic oxidants, and 3 – atmospheric impacts of hydraulic fracturing. Through environmental chamber experiments and chemical reaction modeling I quantified the gas-particle partitioning of organic nitrates as well as the hydrolysis rate of condensed organic nitrates. These interactions are important in understanding total PM levels as well as NOx recycling – the breakdown of organic nitrates to regenerate NOx that was previously removed from ozone production, which in turn is necessary for accurate forecasting of ozone levels. I collected ambient measurements near Houston, TX in September 2013 as part of DISCOVER-AQ (http://www.nasa.gov/mission_pages/discover-aq/index.html). These measurements provide valuable insight to the processes that leads to PM formation in the area. There is evidence that the interaction between biogenic organic compounds and anthropogenic oxidants has an important effect on PM levels. A diurnal cycle of increased nighttime PM concentrations suggests that reactions between terpenes and the nitrate radical significantly contribute to PM. A poorly characterized source of emissions from hydraulic fracturing activity are atmospherically vented storage tanks for flowback wastewater. Emissions of ammonia and hydrocarbons are observed as samples evaporate from 12 different wastewater samples from the Permian Basin. Through chamber experiments I tested the potential of these evaporated mixtures to produce PM in the presence of an atmospheric oxidizer, NOx and seed particles, and I observed significant formation of organic and ammonium nitrate PM.